The present invention relates to a speaker edge disposed around a vibration plate (viz., conical body) of the speaker and adjoined to the inner periphery of a frame so as to hold the vibration plate in its correct position where it is not hindered from freely vibrating. In particular, the present invention relates to a speaker edge that is produced using a thermosetting composition and a mechanically foaming means, and also relates to foam-molding method and system and a foam-molding apparatus, all being designed to manufacture the speaker edge.
Usually, each speaker has a main vibration plate 7 whose periphery is connected by a speaker edge 7a to a frame 16, as shown in FIG. 1. The main vibration plate 7 taking this position is not hindered from vibrating in an axial direction. The speaker edge 7a has in cross section an arcuate portion (viz., corrugation) 115 that is curved upward or downward between its outer and inner peripheries, lest the vibration plate 7 should suffer any difficulty when vibrating transversely.
In some cases, the prior art speaker edges 7a have been formed of a vulcanized rubber foam. In other cases, a thermoplastic resin such as an acrylic polymer, a polycarbonate, a polyurethane, a polyester, a polyolefin or the like has been molten and injection molded around the periphery of each vibration plate 7. Alternatively, a foamed polyurethane block has been severed into slabs, each being subsequently sliced into thin sheets of a given thickness so as to be heated and pressed in a mold to give the speaker edge 7a. 
The molten thermoplastic resin will be kept at an elevated temperature from about 200xc2x0 C. to 300xc2x0 C. when injection molding the speaker edge 7a. Thus, the vibration plate 7 being bonded to and made integral with this edge within a couple of mold segments 41 and 42 is likely to suffer from thermal deterioration.
It is a further problem that the vulcanized foam rubber has failed to provide a sufficiently high ratio of foaming, thus increasing overall weight of the speaker edge and vibration plate bonded thereto. In such an event, the frequency-to-sound pressure property will be rendered inferior to those which have been made lighter. In addition, the speaker edge of such a vulcanized foam rubber has to be adhered to the vibration plate, using a highly sophisticated adhesion technology and nevertheless encountering difficulties in adhesion process.
FIG. 10 illustrates a speaker edge 7axe2x80x2 (hereinafter called xe2x80x98thermally compressed article of polyurethane foam slab/sheetsxe2x80x99) whose arcuate portion has basal ends 7b. The rear (convex) corner of each basal end 7b is thermally stretched to have a lower density, during the pressing process within a mold. Consequently, the front (concave) corner of each basal end 7b is rendered higher in density, due to compression. Such an unevenness in density produced between the front and rear corners or surface layers has undesirably impaired strength and durability. The inner periphery of such a speaker edge 7axe2x80x2 vibrates in unison with the periphery of vibration plate 7, but with the outer periphery of said edge 7axe2x80x2 being retained in place by the frame 16. As a result, fatigue of material will proceed exclusively in one of those basal ends 7b, adjacent to the frame 16. The thinned region 7c of each arcuate portion basal end has not necessarily been satisfactory in strength.
Each slab of polyurethane foam is not free from unevenness from region to region, due to the foaming process itself. The sheets sliced from such a slab for forming the thermally compressed article 7axe2x80x2 of polyurethane foam do inevitably differ in density, corresponding to the regions in said slab. Thus, speakers 1 comprising the thermally compressed speaker edges 7axe2x80x2 each composed of those slab sheets will show a considerable variation in their minimum resonance frequency fo, varying quality or performance of them. For example, variation of fo measured for 100 samples was found xc2x115 Hz.
FIG. 18 is an enlarged cross-sectional scheme of the thermally compressed speaker edge 7axe2x80x2 made of the slab sheets 117 shown in FIG. 10. As seen in FIG. 18, a surface layer has been depressed during the thermally compressing molding process so that void cells in said layer are collapsed to give a harder and denser skin 68. An apparent boundary will be recognized between this skin and an inner regularly foamed core. Physical properties change sharply across the boundary, increasing amplitude of the resonance and causing a distortion in tone quality.
An internal texture of the thermally compressed slab/sheets article 7axe2x80x2 will be seen in FIG. 3, that is a photo taken using a microscope of 60 magnifications. There will be observed a surprising visual difference between this photo and FIG. 2 that is another microscopic photo of the same magnifications showing the speaker edge 7a of the resent invention.
Speakers built in automobile car doors or the like must be waterproof, whereas polyurethane slabs absorb water from their outer surface. The prior art speaker edges 7axe2x80x2 that are polyurethane slab sheets thermally compressed are therefore not waterproof to a sufficient degree. In order to resolve this drawback, it has been proposed to coat the surfaces of speaker edges with a fluoride resin. However, in view of the open-cell structure of those prior art speaker edges, any excessively thick coating that will clog the cell openings with the fluoride resin should be avoided. Thus, any satisfactory waterproofing finish has not been available, despite a noticeably raised manufacture cost.
The preceding Japanese patent application No. 11-61879 discloses an improvement in the described prior art speaker edges. According to this proposal, a two-fluid reactive composition comprising an isocyanate and a polyol will be fed into a pair of male and female segments of a mold, through a stirring mixer. Within the mold, the two ingredients will react one with another to foam and solidify, for example at about 60xc2x0 C. Due to such a low temperature, each cycle of molding the speaker edge will necessitate an undesirably long time, for example 2 minutes. Further, the two-fluid ingredients once blended together will solidify so soon that the mixer is jammed with them, unless immediately transferred to the mold. Process management, including process control of interrupted operation, will thus be rendered intricate and troublesome. The tow-liquid type raw material is so susceptible to ambient condition such as humidity that the foaming ratio tends to vary between batches or lots, making it difficult to ensure uniform quality.
The present invention was made in view of the drawbacks inherent in the prior art speaker edges and the prior art method of making same. A novel speaker edge provided herein is made of a thermosetting composition that is a mixture of main ingredients, wherein the main ingredients are a polyurethane prepolymer and a latent hardener, and the latent hardener is an inactivated solid polyamine. In manufacture of the speaker edge, a gas will be dispersed in the thermosetting composition, prior to feed thereof into a female mold segment heated to a temperature below the critical thermosetting temperature. Subsequently, a male mold segment that has previously been heated to a higher temperature above the critical temperature will be pressed and fitted in the female segment so that the ingredients react with each other to solidify within the mold. In other words, the thermosetting composition in the invention is of the one-liquid type and capable of self-foaming by virtue of the gas mechanically dispersed in said composition, whereby it can be molded directly around the main vibration plate so as to foam and solidify surrounding the periphery hereof.
Such a one-liquid type thermosetting composition of the invention can be injected into a mold either continuously or intermittently, and much more smoothly than in the case of the patent application No. 11-061879. Interruption of the molding process can be managed more easily and at any time wanted. The composition need not be fed to the mold immediately after the step of blending the isocyanate and polyol, thereby diminishing material loss. There will be produced no flashes or waste around the molded piece to be severed therefrom, so that consumption of raw materials can now be reduced and any extra control is not needed in the molding process, also lowering manufacture cost. The thermosetting takes place instantly upon heating to a temperature above the critical temperature to give speaker edges of uniform quality. Thus, the foam-molding method provided herein to produce the speaker edges can be carried out by easier operations and nevertheless decreasing the amount of industrial wastes.
A first species of the present invention provides a speaker edge made of a thermosetting composition that is a mixture of main ingredients, wherein the main ingredients are a polyurethane prepolymer and a latent hardener, and the latent hardener is an inactivated solid polyamine. A gas will be dispersed in the thermosetting composition, prior to feed thereof into a mold, so that the composition foams and solidifies itself therein to give the speaker edge. The thermosetting composition is of the one-liquid type in which the gas is mechanically dispersed to subsequently foam the composition in a simple physical manner.
A second species of the present invention provides such a feature that the foamable thermosetting composition is fed to the mold and around the main vibration plate so that the speaker edge thus formed as defined in the first species is directly and spontaneously adhered to and integral with the periphery of said plate.
A third species of the present invention provides such a feature that, in the speaker edge as defined in the first or second species, internal void cells are physically produced by instant expansion of the gas bubbles that have mechanically been dispersed in the composition, upon injection into the mold where each bubble""s internal pressure is allowed to equilibrate with atmospheric pressure. The foamed structure produced in this manner may consist of closed cells only, or consist of closed cells and open cells in mixture.
A fourth species of the present invention provides such a feature that, in the speaker edge as defined in any one of the first to third species, the void cells contained therein are of a size falling within a range of 1xcexc to 100xcexc. Such a fine and uniform size of void cells is realized herein by virtue of the physical foaming of fine gas bubbles mechanically dispersed in the thermosetting composition, which bubbles are then allowed to expand in the due to equilibrium between the internal pressure of each bubble and the atmospheric pressure.
A fifth species of the present invention provides such a feature that, in the speaker edge as defined in any one of the first to fourth species, the void cells as defined in any of the first to fourth species have diameters whose average is 20xcexc and which are distributed beside this average. Owing to mechanical dispersion of the gas and physical expansion thereof within the speaker edge, the void cells are of uniform diameters as indicated by a sharp and histogram-like graph shown in FIG. 12.
A sixth species of the present invention provides such a feature that, in the speaker edge as defined in any one of the first to fifth species, it has a density falling within a range of 0.15-0.9 g/cm3. The foaming process relying on the mechanical dispersion and physical expansion of gas bubbles does facilitate precise control of the foaming ratio.
A seventh species of the present invention provides such a feature that, in the speaker edge as defined in any one of the first to sixth species, it may have a skin layer whose surface is embossed with the pattern of the mold""s internal surface.
An eighth species of the present invention provides such a feature that, in the speaker edge as defined in any one of the first to seventh species, it may have the skin layer that smoothly continues to an inner core of said edge, without any apparent or distinctive boundary intervening between them. This is because the void cells are scarcely collapsed within the mold for producing the foamed speaker edge, thus ensuring uniform distribution of cells.
A ninth species of the present invention provides such a feature that, in the speaker edge as defined in any one of the first to eighth species, it may have an arcuate portion whose thin basal ends are at least of the same density as that of the remaining thicker regions. This feature results from the fact that any already foamed article is not pressed in the mold, but an unfoamed material mass is foamed and solidified in the mold. Thus, the arcuate portion has an overall density equal to or higher than that of adjacent body regions of said speaker edge, thus affording smooth and even transmission of vibration.
The present invention further provides, in its tenth species, a method of making a speaker edge. This method comprising the steps of preparing a thermosetting composition whose main ingredients are a polyurethane prepolymer and a latent hardener, the latent hardener being an inactivated solid polyamine, then mechanically dispersing a gas throughout the thermosetting composition, thereafter injecting this composition into a female mold segment heated to a temperature below the critical thermosetting temperature, and subsequently putting a male mold segment in the female segment, wherein the male segment is heated to a higher temperature above the critical temperature so that the ingredients react with each other to solidify within the mold while being foamed. In practice, the female mold segment may either be heated to the temperature below the critical temperature prior to or immediately after injection of the thermosetting composition, or alternatively be heated at any desired point of time but quickly in a short time after injection. On the other hand, the male segment of the forming mold may either be previously heated to the other temperature above the critical one, or be heated instantly upon press-fitting of the male segment in the female one. The foamed and solidified speaker edges can now be produced at a higher rate and at a surprisingly improved manufacture efficiency.
An eleventh species of the present invention provides such a feature that, in the method as defined in the tenth species, it may utilize a high-frequency induction heater for heating the mold so as to efficiently solidify and foam the thermosetting composition therein. This induction heater will raise the temperature in an instant to thereby shorten the cycle time spent to heat mold.
The present invention still further provides, as its twelfth species, an apparatus for carrying out the method of making from a thermosetting composition a speaker edge as defined hereinbefore. This apparatus comprises:
#1. a suction device linked to a piston-type pump having a cylinder in which the piston reciprocates, the device acting to suck air into the cylinder during suction stroke of the piston;
#2. a feed device for charging the cylinder with the composition after the cylinder is filled with the gas;
#3. a stirring device for mechanically mixing with the composition with the gas during exhaustion stroke of the piston;
#4. a compression device for injecting the gas-dispersed thermosetting composition into a female segment of a mold forming the speaker edge, wherein the female segment is heated to a temperature below the thermosetting critical temperature;
#5. a pressing device for fitting a male segment in the female segment, wherein the male segment is heated to another temperature above the thermosetting critical temperature; and
#6. a molding device for foaming and solidifying therein the foamable thermosetting composition.
A thirteenth species of the present invention provides such a feature that, in the apparatus as defined in the twelfth species, it may utilize as or in connection with the molding device a high-frequency induction heater to solidify and foam the thermosetting composition. This induction heater will raise the temperature in a shortened time and at a lowered cost.
The present invention does also provide as its fourteenth species a system for making from a thermosetting composition a speaker edge. This system comprises:
(1.) a suction process using a piston-type pump that has a cylinder in which the piston reciprocates, the process being designed to suck air into the cylinder during suction stroke of the piston;
(2.) a feed process for charging the cylinder with the composition after the cylinder is filled with the gas;
(3.) a stirring process for mechanically mixing with the composition with the gas during exhaustion stroke of the piston;
(4.) a compression process for injecting the gas-dispersed thermosetting composition into a female segment of a mold forming the speaker edge, wherein the female segment is heated to a temperature below the thermosetting critical temperature;
(5.) a pressing process for fitting a male segment in the female segment, wherein the male segment is heated to another temperature above the thermosetting critical temperature; and
(6.) a molding process for foaming and solidifying therein the foamable thermosetting composition.
In this system, the reciprocal piston-pump is used to intermix the air with the thermosetting composition for forming the speaker edge. The gas is continuously dispersed in the composition which is subsequently allowed to foam itself in a successive manner. In contrast with the prior art chemical method of foaming the composition, the foaming is done herein in a physical manner. The piston-pump enables a highly accurate blend ratio of the gas to the composition, making it possible to precisely control the foaming degree of the resultant product. Either the forming mold or the thermosetting composition itself is heated in a direct manner, thereby accelerating the solidification of said composition and improving manufacture efficiency.
A fifteenth species of the present invention provides such a feature that, in the system as defined in the fourteenth species, it may utilize, in the molding process for foaming and solidifying therein the foamable thermosetting composition, a high-frequency induction heater. This induction heater employed in the system of the invention will instantly and directly heat said composition injected into the mold. This system is adapted to a case wherein the mold is not heated, but solely the composition itself is heated.
The present invention does further provide as its sixteenth species a speaker comprising a vibration plate built therein and a speaker edge, wherein the speaker edge is made of a thermosetting composition whose main ingredients are a polyurethane prepolymer and a latent hardener, with the latent hardener being an inactivated solid polyamine. A gas will be dispersed in and throughout the thermosetting composition, prior to feed thereof into a mold, so that the composition foams and solidifies itself therein to give the speaker edge. Such a speaker thus manufactured efficiently does scarcely show distortion in tone quality, its resonance frequency in the bass zone being not lowered too much, and is of an improved resistance to heat and water.